(function(doc, win) {

	var docEl = doc.documentElement,
		resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
		recalc = function() {
			
			var clientWidth = docEl.clientWidth;
			if(!clientWidth) return;
			if(clientWidth >= 640) {
				clientWidth = 640;
			}
			if(clientWidth <= 320) {
				clientWidth = 320;
			}
			docEl.style.fontSize = 100 * (clientWidth / 640) + 'px';
		};
	if(!doc.addEventListener) return;
	win.addEventListener(resizeEvt, recalc, false);
	doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);




